Optical Disk Apparatus

Abstract

A servo control of an optical disk apparatus increases a suppression degree of an iterative learning control system, against a frequency disturbance of integer multiple of rotation frequency in a predetermined rotation phase range including a range, in which a servo deviation is detected, of the rotation phase.

Description

INCORPORATION BY REFERENCE[0001]The present application claims priority from Japanese application JP2009-002122 filed on Jan. 8, 2009, the content of which is hereby incorporated by reference into this application.BACKGROUND OF THE INVENTION[0002]The present invention relates to an optical disk apparatus for recording and / or reproducing information in and / or from an optical disk.[0003]As one of the causes of a servo follow-up deviation in the optical disk apparatus, a periodic disturbance is included therein, which is caused by rotating the optical disk. There has been a method that makes a servo gain high to increase an allowable disturbance amount, as one of the methods for enhancing a follow-up performance against the periodic disturbance.[0004]In contrast, JP-A-2001-84620 has disclosed that “It is necessary to raise a cutoff frequency since a servo band is more broadened when a reproduction speed of DVD is made high. For example, an oscillation is inevitable when a resonance app...

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Benefits of technology

[0013]The deviation component has a low frequency in comparison with the disturbance component such as a defect and scratch, therefore, it is effective to follow up the track with increase of the servo gain, as a measure. On the other hand, the disturbance component of the defect and scratch has high frequency, therefore, the servo gain is turned down to make a servo response small, and the follow-up should not be performed forcibly, which becomes an effective measure.

[0014]The deviation component has a signal waveform synchronized with the rotation period so that it can be represented by a sum of the rotation frequency and its high-order component operated by Fourier transform, therefore, it is possible to suppress the deviation component by the iterative learning control.

[0021]From the above description, the inventor(s) has assumed an optical disk apparatus which is difficult to turn up the servo gain from the steady state, and has found that it is demanded that a configuration of the optical disk apparatus has both a steady suppression performance of the deviation and a smooth suppression performance for the deformation of deviation waveform at every rotation period to thereby suppress the deterioration of follow-up performance in minimum even when the rotation asynchronous component is further added to the servo system.

[0026]Further, the JP-A-2001-126421 has proposed as still another method. In this method, the configuration of iterative learning control system provides an adder for adding an output signal of the delay memory device to the position error signal which is not delayed to obtain the new inner state signal and output to the delay memory device. The gain in a multiplier, which multiplies a gain by an output signal from the iterative learning control, is further made small so that the deterioration of follow-up performance is avoided for the rotation asynchronous component. However, there is a drawback that a convergence of the learning becomes slow in this method. For this reason, it is difficult to respond to the case where the waveform of deviation component is varied at every rotation period on the performance of iterative learning control.

[0027]In light of the above-mentioned problems, an object of the invention is to enhance the track follow-up performance of the optical disk apparatus using the iterative learning control.

[0029]According to the invention, the track follow-up performance can be enhanced in the optical disk apparatus.

Problems solved by technology

A first problem is that it is difficult to take simultaneous pursuit for a suppression of the component so called deviation and a servo stability on the high operation speed.

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